Power in the form of torque has been transferred from one location to another for thousands of years. In some of its earliest forms, belts formed of cordage-like material, animal leather and the like, were used to transmit torque at a distance to other objects. The present invention relates to a means which has been developed for reducing the slip experienced between resilient, elastomeric drive belts, such as flat belts, and V-belts, and which further mechanically cooperate with both pulleys and sheaves. As should be appreciated, the term “pulley” and “sheaves” typically have different meanings in different industries. In this document the word “sheave” is typically used with V-belts whereas “pulleys” are discussed in terms of either being a variable width sheave used, for example, in variable speed transmissions, or they are used with flat belts. In the present application, the term non-synchronous drive belt includes drive belts fabricated, at least in part, from synthetic, elastomeric material and further excludes synchronous belts such as timing belts which do not slip, but lack a self-protective clutching action when exposed to shock and power over-loads.
With regard to the present invention it should be understood that the phenomenon of belt slip is distinct from that of belt creep. Belt creep which typically occurs at a rate of about 0.5 to about 1%, is an inch worm—like effect which occurs at any given point along the path of belt movement as the non-synchronous drive belt moves through various tension gradients. Belt slip, on the other hand, results in the generation of elevated temperatures and other deleterious effects being imparted to the non-synchronous drive belt which forcibly engages a pulley or sheave.
Sheaves and V-belts are arranged to transmit mechanical power at high efficiencies. However, to achieve this objective, there must not be any appreciable belt slippage and only a certain amount of belt creep. The ability of a V-belt and sheave systems to perform in typical operational environments, as intended, has long posed a challenge for designers and users. In this regard, designers of drive systems have often failed to fully account for the real world interplay of variables like vibration, contamination, uncertain loads, and environmental conditions which diminish the amount of transmissible mechanical power to below expectations. Many have speculated that marketing pressures to keep purchasing costs low for such products have resulted in a pervasive lack of design robustness and reserve margin in the non-synchronous drive belts which are currently commercially available.
Those who are skilled in the art readily recognized that there is a natural tendency for end-users to ignore V-belt and sheave systems. Consequently, such systems tended to receive reactive rather than proactive and scheduled maintenance. This has caused incalculable losses due to wasted energy, costly parts replacement and lost productivity. A solution has long been needed to address these problems, but it has proven elusive. In this regard, V-belt and sheave systems tend to rely solely upon friction developed between the polymeric or elastomeric materials employed in these non-synchronous drive belts, and the accompanying metal sheave or pulley to function at some acceptable operational level. The coefficient of friction in these systems vary significantly in real world applications. For example, the coefficient of friction values are thought to range from about 0.2 for wet or dirty environments, to about 0.3 during normal operating conditions. In typical V-belt systems with their 40 degree included V-shape, the wedged coefficient of friction is thought to average about 0.5 under typical field conditions. Although belt slip is very common, all V-belt/sheave systems function properly only when they experience belt creep, and suffer no appreciable belt slip. As noted above, belt slip degrades real-world performance and produces deleterious friction-generated waste in the form of thermal power or what has been termed “heat load.” Accordingly, a key object of designers through the years is to ensure that V-belts remain taunt with adequate tension for a reasonably long interval between scheduled maintenance. This objective is often subverted by a shortcoming inherent in common belt tensioners, and which typically use a spring to force an idling wheel into a force engaging location, mid-span, and into the side of the rotating non-synchronous drive belt.
The shortcomings in belt tensioners are well known, and they arise from the way in which these devices become increasingly ineffective as a system to prevent the problems associated with the generation of heat during operation, and which is caused by belt relaxation and expansion. Belt expansion, in turn, causes the idler device to deflect further into the belt path. This extra deflection diminishes the mechanical advantage provided when the belt and the associated pulleys are first tensioned into a proper relationship.
Over time, and due to the effect of the belt tensioner, a belt can become longer, and cause a corresponding amount of increasing belt slippage. Consequently, periodic maintenance is required to readjust the belt/drive system. As should be appreciated, this act of readjustment seems to be a bothersome shortcoming to many end-users. As a result, many end-users often respond to increasing belt slippage by moving the sheaves tighter, and further apart, thus increasing the strand tension often beyond industry recommended standards. Many users inevitably discover that by doing this act they dramatically diminish both the belt life, and the useful life of the bearings which rotatably support the pulley or sheave.
In addition to the problems noted above, V-belt systems often include insufficient reserve margin. In this regard, such V-belt systems are usually employed in high-powered mechanical systems. Further, these systems are often operated in harsh environments where adding robustness to the overall system poses cascading engineering consequences, such as, significant added costs, and increased use of space. Such mechanical systems have typically employed sophisticated belt tensioning devices that maintain essentially constant belt tension. However, real-world loads on these mechanical devices can be unpredictable, and can often be greater than what has been envisioned by engineering designers. Consequently, belt slip occurs even when systems are tensioned to appropriate and recommended manufacturer specifications.
Many operators of agricultural equipment are familiar with this phenomenon. If a belt drive system is equipped with a belt slip indicator, the operator has little choice when a belt slip indicator alarms but to reduce load (reduce engine power or somehow lessen the load demand on the system). In high power systems with no slip indicator, or one that is disregarded, excessive and persistent belt slip not only significantly diminishes the life of the non-synchronous drive belt, but also results in further system inefficiency and reduced productivity. Persistent belt slip ultimately results in system performance degradation often to the point of catastrophic system failure. If an adverse amount of heat is generated during operation, production or operations must typically be halted to allow the overall system to cool down. As those skilled in the art will recognize, ignored or unnoticed belt slip will often lead to a belt failure.
The problems associated with belt creep, and belt slippage, are well known. Belt slip causes three types of long term performance degradation which further exacerbates the problems noted, above. As a first matter, elastomeric, synthetic and non-synchronous drive belts that run or experience hot operating temperatures due to belt slip and/or creep will eventually harden from a durometer of Shore 70A, to a slick, urethane-like Shore 45D. The underlying mechanism of belt hardening is well known, and is one of thermo-oxidation which causes a post-process molecular cross-linking. As will be understood, the very high temperatures arising from prolonged and excessive belt slip can rapidly, that is, in a matter of weeks, harden and glaze non-synchronous drive belts to a point where they must be replaced because they have less friction, and even more belt slip than what was experienced during their original installation. Secondly, belt slip is known to be a mildly abrasive process that slowly polishes (glazes) sheaves and associated pulleys. Additionally, metal smearing can occur with sheaves manufactured from aluminum, and also can occur in ones fabricated from steel under certain circumstances. Thirdly, the abrasive action that causes the glazing of sheaves, and pulleys, can also produce or form undulations in the V-shaped profiles of the sheaves which are installed. These undulations diminish the belt's wedging action. Several interacting phenomena are at play when this occurs in a drive belt system. Suffice it to say that a glazed sheave having profile undulations is especially incompatible with a thermo-oxidized, non-synchronous drive belt.
The prior art is replete with various prior art references which teach assorted ways to produce a high coefficient of friction surface on a sheave or pulley. Some of these teachings have entailed the creation of macro-sized features such as ribs, slots and dimples on the belt contact surface of the respective sheaves or pulleys. However, these structures have all been shown to accelerate belt wear. Other prior art references have taught the creation of micro-sized texturing on the metal sheave surfaces. However, this texturing has also accelerated belt wear. Further, many users have discovered that this fine texturing often was worn away by the belt-slip action of the non-synchronous drive belt. Other possible solutions to the problems noted, above, and which were designed to obtain a high coefficient of friction surface, that didn't wear away, involved the embedding of a wear-resistant abrasive, that being, a ceramic or other mineral, into the sheaves themselves. These prior art embodiments featured particle sizes that could be seen with the naked eye, whereas others featured very small particles which could not be readily visibly discerned. However, since non-synchronous drive belts running on abrasive coated sheaves boasting a high coefficient of friction still experience belt creep, and further since V-belts dynamically wedge in or out of a 40° included angle at least four times per belt revolution, abrasive coated sheaves experience poor belt life. This is unsurprising since one of the defining characteristics of abrasive powders, besides being harder than the materials being abraded, is that they have sharp cutting edges.
Therefore, what is needed to solve the aforementioned problems is to provide a surface or surface treatment that improves the coefficient of friction between a sheave or other drive pulley and drive belt, and that further doesn't simultaneously abrade the belt, and which additionally allows the drive belt to run at a cooler temperature, and with less thermal oxidation. In high power mechanical applications, a significant improvement in the coefficient of friction would permit a reduction in the number of grooves formed in the sheave; and a cascading series of engineering benefits would ensue. Ideally, a solution to this long felt need would also make sheaves and pulleys resistant to glazing and groove profile changes.
An invention which avoids the detriments associated with the prior art practices and devices utilized, heretofore, is the subject matter of the present application.